Rotation position information on an AC rotary machine and information on currents flowing through the AC rotary machine are necessary for accurately controlling a rotation operation of the AC rotary machine. The rotation position information is obtained by separately mounting a rotation position sensor to the AC rotary machine. However, when the rotation position sensor is separately provided, there is a great disadvantage in terms of cost, space, and reliability. Therefore, a sensorless configuration that uses a rotation position estimated value instead of the rotation position sensor is required.
Moreover, when the rotation position sensor fails, an operation of the AC rotary machine can be continued by alternatively introducing the rotation position estimated value as the rotation position information. Due to this fact, a rotation position estimation function is required also as a backup device to be used when the rotation position sensor fails.
From this viewpoint, the following related art is known (e.g., refer to Patent Literature 1), Patent Literature 1 relates to a rotary machine including a plurality of sets of a plurality of stators coupled to one another at a neutral point. Specifically, Patent Literature 1 is constructed by estimation means and stator phase separation means.
The estimation means is configured to superimpose a high-frequency voltage signal having a frequency higher than an electrical angle frequency, to thereby estimate the rotation angle of the rotary machine based on a detected value of a high-frequency current flowing through the rotary machine in accordance with the superimposed high-frequency voltage signal. Moreover, the stator phase separation means is configured to make the phases of the currents flowing through the stators different for at least one pair of sets out of the plurality of sets. Further, the estimation means is configured to increase a degree of use of the detected value of the high-frequency current for a current that flows through the stator and has an absolute value equal to or more than a predetermined value.